I found a way to get 1Password for iOS into a "hung" state, unable to login to my account. I reproduced this on two devices (described in the details below), but was unable to reproduce on a device running 1Password 7.2.8 on iOS 12.1.4 (I was signed in normally on this device).
Steps to reproduce
1. Sign in to a 1Password account using the current iOS beta.
2. Close the 1Password app.
3. Login to the web interface.
4. Generate a new secret key.
5. Disconnect all existing devices.
6. Launch 1Password on iOS.
7. Wait for it to figure out what happened and close.
8. Launch 1Password on iOS.
9. Attempt to sign in to the account again by scanning a new QR code.
I should be signed in to 1Password on iOS and able to access my content.
The sign in button turns into a blue background with a spinner and stays this way for 5+ minutes. I was not able to find a way to resolve this situation within the app, but deleting and reinstalling allowed me to sign in within seconds.
1Password Version: 7.3.1 (via TestFlight)
Extension Version: Not Provided
OS Version: iOS 12.4 (16G5027i)
Sync Type: 1Password.com